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IM21.1-9 | Envenomation — PBL Case

CLINICAL SETTING

It is 6 PM in October at a busy district hospital in Andhra Pradesh. The emergency department has one duty medical officer, Dr Karthik, a final-year MBBS intern, and a staff nurse. Ramu Reddy, a 45-year-old farmer, is brought in by his son on a two-wheeler. The son reports that his father was working in a paddy field at around 4 PM when he felt a sudden sharp pain on his right ankle. He looked down and saw a 'fat brown snake with a chain pattern of white-bordered blotches' moving into the undergrowth. His son immediately applied a tight cloth tourniquet above the knee and brought him to the hospital. The journey took two hours. On arrival, Ramu is conscious but appears distressed. His right leg has swelling extending from the ankle to the upper thigh. The tourniquet is still in place. The intern opens the logbook and writes: 'Snakebite — right ankle. Time of bite: 4 PM. Time now: 6 PM. Tourniquet applied.' Dr Karthik enters the cubicle.

Trigger 1: First Assessment: Species, Syndrome, and the Tourniquet

Dr Karthik examines Ramu. The bite site shows two fang marks on the medial aspect of the right ankle with surrounding haemorrhagic blisters and purplish discolouration of the skin extending 8 cm around the wound. The leg is markedly swollen. The tourniquet has left a deep groove; the foot below it appears congested and cyanotic. Ramu reports that he feels nauseated and that his gums have been bleeding for the past hour. Dr Karthik turns to the intern: 'Before we do anything else, tell me what species caused this bite and what syndrome we are dealing with. And what do we do about that tourniquet right now?'

DISCUSSION POINTS

  • Using the morphological description of the snake and the clinical presentation, which of the big four Indian snakes most likely caused this bite? What envenomation syndrome does this species produce, and what is its pathophysiological mechanism?
  • The tourniquet has been in place for approximately 2 hours. What are the risks of removing it rapidly versus removing it slowly? What is the evidence-based recommendation for tourniquet removal in snakebite?
  • Gum bleeding at 2 hours post-bite — what does this sign tell you about the severity of envenomation, and does it change your management decisions at this moment?
Click to reveal Trigger 2: Investigations and the Antivenom Decision (discuss previous trigger first!)

Trigger 2: Investigations and the Antivenom Decision

Dr Karthik removes the tourniquet slowly while the nurse prepares a clean dry glass tube for a 20WBCT. At 20 minutes, the blood in the tube has not clotted. Ramu's BP is 96/60 mmHg, HR is 108/min, SpO2 97% on room air. Blood is sent for CBC, coagulation profile, renal function, and urinalysis. The urine sample is a dark reddish-brown colour. The nurse prepares the antivenom vials and asks: 'Doctor, how many vials, how much dilution, and at what speed?' Dr Karthik hesitates — the hospital stocks 10-vial packs and has adrenaline in the emergency tray. He pauses and says to the intern: 'Walk me through the antivenom decision: is it indicated, and if yes, what are the exact parameters for administration?'

DISCUSSION POINTS

  • List the ASV indications present in this case. Is local swelling an indication for ASV? Explain precisely which findings in this case constitute systemic envenomation.
  • Describe the correct technique for administering Indian polyvalent ASV: number of vials for initial dosing, dilution, route, infusion rate, and the pre-requisite safety measure that must be completed before the infusion begins.
  • The urine is dark reddish-brown. What does this indicate, and how does this finding affect your organ-specific monitoring and management plan?
Click to reveal Trigger 3: Adverse Reaction During Infusion (discuss previous trigger first!)

Trigger 3: Adverse Reaction During Infusion

Ten minutes after starting the ASV infusion (10 vials in 200 mL normal saline), Ramu develops generalised urticaria, complains of tightness in his chest, and his BP drops to 78/50 mmHg. His SpO2 falls to 92%. The nurse shouts: 'Doctor, he is having a reaction!' Dr Karthik immediately stops the infusion. The intern is frozen. 'Tell me — step by step — what we do right now. What drug, what dose, what route, and in what order?'

DISCUSSION POINTS

  • Classify this reaction. Is this early anaphylaxis, a pyrogenic reaction, or a serum sickness reaction? How do you distinguish them clinically?
  • Describe the immediate management sequence: name each drug, its dose, its route, and the rationale for the order in which you give them. Why is the route of adrenaline critical?
  • Once Ramu is stabilised, the remaining question is: should the ASV infusion be restarted, and if so, how? What modification is made to the subsequent infusion?
Click to reveal Trigger 4: Six Hours Later — Response Assessment and a New Problem (discuss previous trigger first!)

Trigger 4: Six Hours Later — Response Assessment and a New Problem

The anaphylaxis resolves with adrenaline IM and supportive care. The ASV infusion is restarted at a slower rate and completed. Six hours after the initial ASV dose, a repeat 20WBCT is performed. The blood still does not clot at 20 minutes. The coagulation results return: PT >120 seconds, fibrinogen undetectable, D-dimer markedly elevated. The renal function shows creatinine 2.8 mg/dL (baseline not known). Urine output over the last 6 hours is 180 mL. The family asks: 'He had antivenom — why is his blood still not clotting? And can we give him blood thinners to fix the clots in his blood?' Dr Karthik explains the situation to the family and then turns to the intern for the management plan: 'What do we do now? Is more antivenom needed? Do we give blood products? And what about his kidneys?'

DISCUSSION POINTS

  • The 20WBCT is still non-clotting 6 hours after ASV. What does this mean, and what is the correct management response? At what point would you consider adding blood products, and which products?
  • Explain VICC pathophysiology to the family at an appropriate level — why did antivenom not immediately restore clotting, and why are 'blood thinners' not the treatment?
  • Ramu has oliguria and rising creatinine. What are the mechanisms of AKI in Russell's viper envenomation? What is your specific management plan for the renal failure, and when would you consider renal replacement therapy?

Group Task Assignments

  • Construct a comprehensive pre-hospital and in-hospital management protocol for snakebite that could be printed as a laminated one-page reference card for rural primary health centres in Andhra Pradesh. Include: immediate DO and DO NOT measures, 20WBCT technique, ASV indications, dose and infusion parameters, and anaphylaxis management.
  • Design a community education module for paddy farmers in a snakebite-endemic district. Cover: peak season and peak hours for bites, recognition of the big four species, what to do immediately after a bite, what NOT to do, and which hospital to go to. Address specifically why tourniquets and incision/suction are harmful.
  • Debate the following proposition from the perspective of a district hospital medical officer: 'In resource-limited settings with unreliable ASV supply, withholding ASV from patients with only haematotoxic coagulopathy (but no active bleeding) and awaiting clinical deterioration is a reasonable strategy.' Critically evaluate this position using evidence.
  • Create a monitoring flowsheet for a patient admitted with Russell's viper envenomation. Include: which parameters to monitor, their frequency, the threshold values that should trigger specific management escalations, and the criteria for safe discharge.

Learning Issues

Research these questions and bring your findings to the discussion.

  1. [IM21.1] What are the four medically significant Indian snakes (the big four), what are their distinguishing morphological features, and which envenomation syndrome does each produce?
  2. [IM21.2] What are the evidence-based correct and incorrect first-aid measures for snakebite, and what is the specific harm caused by tourniquet application?
  3. [IM21.6] What is the 20-minute whole-blood clotting test (20WBCT), what are the technical requirements for its accuracy, and how is it used to monitor antivenom response?
  4. [IM21.7] What are the indications, dose, route, infusion rate, and adverse reaction management protocol for Indian polyvalent anti-snake venom?
  5. [IM21.3] What is the systematic approach to stabilisation of a snakebite patient on arrival, and how does the ABCDE framework integrate with snakebite-specific assessment?